1. Field of the Invention
The present invention relates to a digital cordless telephone system and, more particularly, to a digital cordless telephone system having a communication mode switching device, which can connect a telephone unit either to a master unit connected to a personal or private line or to a radio base station connected to a public line through a time-division multiplex channel.
2. Description of the Prior Art
A conventional digital cordless telephone system is constituted by a plurality of radio base stations connected to a public line, a master unit connected to a personal line, and a subsidiary unit which is connected either to one of the radio base stations or to the master unit through a time-division radio channel so as to transmit/receive speech and control data. In the range in which the subsidiary unit can be connected to both the radio base station and the master unit, the user must manually switch the mode of using the public line for connection and the mode of using the personal line by a key operation or the like.
In the digital cordless telephone system, the subsidiary unit can be connected either to the radio base station connected to the public line or to the master unit connected to the personal line through a time-division multiplex radio channel. The charge for the public line is higher than that for the personal line.
As described above, in order to select the public line or the personal line for connection, the user must perform a key operation or the like.
In the range in which the subsidiary unit can be connected to both the radio base station and the master unit, the subsidiary unit may be connected to the public line, for which the charge is high, if the user does not switch the connection lines, even though the subsidiary unit can be connected to the personal line. This will increase the charge for lines and the like.